1. Field of the Invention
The present invention relates to a ball stud subjected to a rust-inhibiting treatment.
2. Background Art
A ball joint is constituted to include a ball stud having a ball at one end of a rod-shaped stud, and a socket for fitting the ball of the ball stud. The ball stud is, for example, connected to other members in the following manner; the ball is tightly fitted through a resin sheet in the socket and the exposed portion of the stud protruding from the socket is covered with a covering and an externally threaded portion formed at the other end of the stud is fixed to other members. As a result, the ball stud usually has little exposed portion, and need not be rust-proofed. Thus, most ball studs have not been subjected to rust-inhibiting treatment.
In recent years, however, requirements for the specifications have risen to the level requiring rust-inhibiting treatment on the ball stud or at least on the stud portion protruding from the socket. It is conceived that the various rust-inhibiting means known in the prior art, such as means for applying rust-inhibiting paint only to the stud. In this case where the means is the rust-inhibiting paint, the application of the rust-inhibiting paint-exclusively to the stud portion is so difficult as to cause another problem that the ball has to be cleared of the rust-inhibiting paint. Thus, JP05-062726 U has disclosed a technique for continuously forming a resin film over the surface of the stud and the surface of the ball.
In the ball stud of JP05-062726 U, both the surface of the stud and the surface of the ball are continuously coated with a resin softer than that of the resin sheet (in JP05-062726 U referred to as bearing 2) to be fitted in the socket. It is disclosed that the resin film formed on the ball need not be removed to lower the cost for the manufacture. It is also disclosed that the resin film acting to inhibit the rust is softer than the resin sheet in the socket so that the sliding resistance to the ball can be lowered. It is also said that it is possible to improve the qualities of the ball joint constituted by assembling the ball stud with the socket, e.g., the torque transmissivity or the endurability of the ball joint.